Crankshaft journal fillet quenching process

The crankshaft is the heart of the engine, and its quality directly affects the quality of the entire vehicle. Crankshaft journals for passenger car engines typically use medium-frequency induction hardening. FAW Group mainly uses rotary quenching technology for surface heat treatment of crankshafts, treating the main journals, connecting rod journals, flanges, and thrust faces. This technology has a history of more than 20 years. With the advancement of technology, the requirements for crankshaft heat treatment are becoming increasingly stringent. Now, most well-known automobile and diesel engine manufacturers have begun to strengthen the fillets of crankshafts, which can significantly improve the service life of the crankshaft and the overall quality of the vehicle.

In traditional production methods, crankshafts are not fillet quenched. However, crankshafts typically fail by fracture at the fillet, which is the weakest and most stressed part. The forces acting on a crankshaft during operation are quite complex. The main journals, connecting rod journals, and crank arms experience different stresses, but mainly endure repeated bending and torsional loads. The main and connecting rod journals also experience intense friction. Crankshaft damage primarily involves fatigue-induced fracture and journal wear. Therefore, improving crankshaft fatigue strength is our top priority.

Crankshaft fractures are mostly fatigue fractures, and the fatigue source is located at the fillet of the connecting rod journal lower stop point R, where the stress is greatest. Therefore, after induction hardening of the crankshaft journal, the journal hardness can be increased, improving its wear resistance. Fillet quenching of the crankshaft journal significantly improves the crankshaft's fatigue strength, thus greatly reducing the possibility of fatigue fracture. In addition, stress relief annealing of the crankshaft blank effectively eliminates stresses generated during forging, reducing subsequent cold-working stress and releasing stress before quenching, resulting in significantly reduced deformation after quenching.

There are two ways to improve crankshaft fatigue strength: one is to select different materials, such as replacing 45 steel with alloy materials; the other is to use different processes, such as fillet induction hardening of 45 steel crankshafts, fillet rolling of crankshafts, and overall nitriding of crankshafts. Tests have shown that fillet induction-hardened crankshafts have the highest fatigue strength (996 MPa), followed by fillet-rolled crankshafts (890 MPa), and then nitrided crankshafts (720 MPa). The fillet rolling method requires a large investment in supporting equipment, costing over 20 million yuan. The nitriding method is inefficient, and the company lacks the necessary equipment and capabilities. Considering the company's actual equipment conditions, the fillet induction hardening method for crankshafts requires only the addition of an inductor and process adjustments, resulting in the lowest investment and fastest results. It is the most economical and effective method for improving crankshaft fatigue strength. A crankshaft journal fillet quenching process is introduced below.